1. Field of the Invention
The present invention relates to a method of and an apparatus for correcting the sharpness of image information in an image reading system in which a sensor comprising an array of photoelectric transducers arranged in a main direction is moved with respect to a recording medium in an auxiliary direction that is substantially perpendicular to the main direction for thereby two-dimensionally reading image information recorded on the recording medium with the sensor.
2. Description of the Related Art
There is known a radiation image information recording and reading system which employs a stimulable phosphor which, when exposed to an applied radiation (X-rays, xcex1-rays, xcex2-rays, xcex3-rays, electron beams, ultraviolet radiation, or the like), stores a part of the energy of the radiation, and, when subsequently exposed to applied stimulating light such as visible light, emits light in proportion to the intensity of the stored energy of the radiation. In the radiation image information recording and reading system, the radiation image information of a subject such as a human body or the like is temporarily recorded in a stimulable phosphor sheet which comprises a stimulable phosphor layer in the form of a sheet, and then stimulating light such as a laser beam is applied to the stimulable phosphor sheet to cause the stimulable phosphor sheet to emit light representing the recorded radiation image information. The emitted light is photoelectrically read to produce an electric image signal. Based on the image signal, the radiation image information of the subject is outputted as a visible image on a recording medium such as a photographic photosensitive medium or the like or a display unit such as a CRT (Cathode Ray Tube) or the like.
One type of such a radiation image information recording and reading system is known as a point-scan system. In the point-scan system, stimulating light which is moved in a main direction and applied to a stimulable phosphor sheet which is being fed in an auxiliary direction perpendicular to the main direction, and light emitted from the stimulable phosphor sheet in response to the stimulating light is transmitted through a light converging guide to a single photoelectric transducer device such as a photomultiplier or the like, which reads radiation information recorded on the stimulable phosphor sheet in synchronism with the position where the stimulable phosphor sheet is scanned by the stimulating light. In the point-scan system, reading conditions of the optical system from the stimulable phosphor sheet to the photoelectric transducer device are essentially the same in the main direction and the auxiliary direction. Therefore, if the light is emitted from the stimulable phosphor sheet isotropically in the main and auxiliary directions, an image signal produced by photoelectrically converting the light emitted from the stimulable phosphor sheet has substantially equal spatial frequency characteristics in the main and auxiliary directions, and the sharpness of the image is also substantially the same in the main and auxiliary directions.
Another type of a radiation image information recording and reading system is known as a line-scan system. In the line-scan system, the radiation image information recorded on a stimulable phosphor sheet is read by a sensor comprising an array of photoelectric transducers in a main direction while the sensor is moving in an auxiliary direction perpendicular to the main direction. In the line-scan system, since reading conditions differ in the main and auxiliary directions, the spatial frequency characteristics of an image signal produced by photoelectrically converting the light emitted from the stimulable phosphor sheet are generally not equal in the main and auxiliary directions. The spatial frequency characteristics of the image signal in the main direction depend on the focusing capability in the main direction of a light-converging optical system for guiding the light emitted from the stimulable phosphor sheet to the line sensor, and the spacing of the photoelectric transducers of the line sensor in the main direction. The spatial frequency characteristics of the image signal in the auxiliary direction depend on the focusing capability of the light-converging optical system in the auxiliary direction and the reading spacing of the photoelectric transducers in the auxiliary direction.
If the light-converging optical system comprises a lens array of SELFOC lenses arranged in the main direction, then since the positional relationship of an image signal produced by the photoelectric transducers to the lens array in the main direction and the positional relationship of the image signal to the lens array in the auxiliary direction are different from each other, the spatial frequency of the image signal in the main direction and the spatial frequency of the image signal in the auxiliary direction are not in conformity with each other. Therefore, an image produced from the image signal has a sharpness difference between the main and auxiliary directions.
It is a general object of the present invention to provide a method of and an apparatus for correcting image sharpness in an image reading system to produce image information which has substantially the same sharpness in both main and auxiliary directions.
A major object of the present invention is to provide a method of and an apparatus for correcting image sharpness in an image reading system for reading image information from a recording medium by moving a sensor comprising an array of photoelectric transducers arranged in a main direction, in an auxiliary direction with respect to the recording medium, to equalize the image sharpness in the main direction and the image sharpness in the auxiliary direction highly accurately to each other.
Another major object of the present invention is to provide a method of and an apparatus for correcting image sharpness in an image reading system for reading image information with a line sensor comprising an array of photoelectric transducers in a main direction which is combined with a light-converging optical system comprising an array of condenser lenses arranged in the main direction.
The above and other objects, features, and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings in which a preferred embodiment of the present invention is shown by way of illustrative example.